Non-cyclic and Developmental Stage-Specific Expression of Circadian Clock Proteins During Murine Spermatogenesis1

Abstract

The central circadian clock in mammals is housed in the brain and is based on cyclic transcription and translation of clock proteins. How the central clock regulates peripheral organ function is unclear. However, cyclic expression of circadian genes in peripheral tissues is well established, suggesting that these tissues have their own endogenous oscillators. Reproduction is a process influenced by circadian rhythms in many organisms, thus making the testis an attractive model for studying clock function in peripheral organs. However, results addressing cyclic expression of clock genes in the mammalian testis are inconsistent. To resolve this issue, RNA was extracted from testes of mice at various times of day. Expression of the circadian clock genes mPer1, mPer2, Bmal1, Clock, mCry1, and Npas2 was constant at all times. Immunohistochemical localization of mPER1 and CLOCK proteins revealed restricted expression only in cells at specific developmental stages of spermatogenesis. For mPER1, these stages are the spermatogonia and the condensing spermatids. In contrast, CLOCK expression was restricted to round spermatids, specifically within the developing acrosome. Expression of mPER1 and CLOCK was constant at all times of day. These results suggest that clock proteins have noncircadian functions in spermatogenesis. Noncircadian expression of clock genes was also found in the thymus, which, like the testis, is composed primarily of differentiating cells. We propose that cyclic expression of clock genes is suspended during cellular differentiation.

Differential control of peripheral circadian rhythms by suprachiasmatic-dependent neural signals

“…In agreement with some earlier studies (16)(17)(18), but at variance with others (19,21,22), we observed significant circadian variations in relative expression of mPer1, mPer2, and mBmal1 in the testis (Fig. 7, which is published as supporting information on the PNAS web site).…”

The Uterus Sustains Stable Biological Clock during Pregnancy

“…The findings in our present study are consistent with previous reports in that no circadian rhythmicity was detected in adult tissues of the testis and thymus, which have the same property of on-going cellular differentiation as the labyrinth, a fetus-orignated tissue (Alvarez et al 2003). The equal or relatively higher level of Per1 mRNA expression in the labyrinth compared to the decidua can also be explained by the chronic elevated level of progesterone during pregnancy, which has been reported to continuously up-regulate Per1 mRNA expression in vivo (He et al 2007).…”

Day–night cycles and the sleep-promoting factor, Sleepless, affect stem cell activity in the Drosophila testis

“…Consistent with previous findings (32), we did not detect expression of the core circadian clock genes period and timeless in the testis niche or stem cells, which suggests that there is no intrinsic clock function in these cells. Interestingly, murine spermatogonial stem cells also lack cell-autonomous circadian clocks (33), which is in contrast to clock-containing hair follicle, hematopoietic, and intestinal stem cells (14,(34)(35)(36). It is possible that central or peripheral circadian clocks located in the brain, other tissues (2), or even other cells of the testes drive rhythms in the GSCs/CPCs, although the absence of mitotic rhythms in constant darkness argues against this possibility (Fig.…”